UNIT _____: Enzymes and Metabolism Name: _____________________

Metabolism is the sum of the chemical reactions that occur within living organisms.

Define metabolism

Metabolic reactions can be intracellular or extracellular.

State an example of an intracellular metabolic reaction.
State an example of an extracellular metabolic reaction..

Metabolic processes may have a series of steps in the form of a metabolic pathway, which can be linear or cyclical.

Contrast linear metabolic chain reaction pathways with cyclical reaction pathways.
State and example of a linear metabolic pathway (glycolysis; digestion of starch to maltose to glucose)
State and example of a cyclic metabolic pathway (Kreb’s cycle, Calvin cycle)

Metabolic processes can be anabolic or catabolic.

Define anabolic and catabolic.
State an example of an anabolic reaction and a catabolic reaction.

Enzymes are globular proteins that act as catalysts by having an active site to which specific substrates temporarily bind by induced fit.

Outline properties of globular proteins.
Explain the relationship between enzyme structure and enzyme specificity, including the role of the active site.

Coenzymes and cofactors are molecules that help an enzyme to function appropriately.

Define coenzyme and cofactor.

State an example of a coenzyme and a cofactor.

Each step in a metabolic pathway is catalyzed by a specific enzyme.

State the role of enzymes in metabolism.
Define catalysis.

Enzyme catalysis involves molecular motion and the collision of substrates with the active site.

Outline the three stages of enzyme activity.
Explain the role of random collisions in the binding of the substrate with the enzyme active site.

Describe the induced fit model of enzyme action.

Enzymes lower the activation energy by creating a new reaction pathway.

Define activation energy.
State that activation energy is used to break or weaken bonds in the substrate.
Explain the role of enzymes in lowering the activation energy of a reaction.
Interpret graphs showing the effect of lowering the activation energy by enzymes

Temperature, pH and substrate concentration affect the rate of activity of enzymes.

Explain the effects of temperature, pH and substrate concentration with reference to collision theory, temporary and permanent denaturation.
State the effect of denaturation on enzyme structure and function.
Draw and interpret graphs showing the effects of temperature, pH and substrate concentration of the activity of enzymes.

Enzyme action can be inhibited or promoted by the presence of other molecules that temporarily or permanently bind to them, either at their active site or at an allosteric site.

Define enzyme inhibitor.

Inhibitors can be either competitive or noncompetitive.

Contrast competitive and noncompetitive enzyme inhibition.
State an example of a competitive inhibitor
State an example of a noncompetitive inhibitor

The effect of a competitive inhibitor can be reduced by increasing substrate concentration, but this has no effect on noncompetitive inhibition.

Explain why the rate of reaction with increasing substrate concentration is lower with a non-competitive inhibitor compared to a competitive inhibitor.

Metabolic pathways can be controlled by end-product inhibition.

Describe allosteric regulation of enzyme activity.
Outline the mechanism and benefit of end-product inhibition.
Illustrate end-product inhibition of the threonine to isoleucine metabolic pathway.

Design an experimental investigation of a factor affecting enzyme activity.

Identify the manipulated, responding and controlled variables in descriptions of experiments testing the activity of enzymes.
Explain the need to control variables in experimental design.
Describe three techniques for measuring the activity of an example enzyme.

Accurate, quantitative measurements in enzyme experiments require replicates to ensure reliability.

Define quantitative and qualitative.
Determine measurement uncertainty of a measurement tool.
Explain the need for repeated measurements (multiple trials) in experimental design.

Calculate the rate of reaction for enzyme-controlled reactions.

State two methods for determining the rate of enzyme controlled reactions.
State the unit for enzyme reaction rate.
Given data, calculate and graph the rate of an enzyme catalyzed reaction.

Immobilized enzymes are widely used in industry, such as in the production of lactose-free milk.

List industries that use commercially useful enzymes.
Explain how and why industrial enzymes are often immobilized.
State the source of the lactase enzyme used in food processing.
State the reaction catalyzed by lactase.
Outline four reasons for using lactase in food processing.

Metabolism

Definition:

Intracellular Metabolism

Extracellular Metabolism

Metabolic Pathways

A series of ‘steps’ from a starter molecule or precursor toward a final end product.

Each step is catalyzed by a different enzyme.

Linear Pathway

Examples:

Cyclical Pathway

Examples:

Anabolic Pathway

Example:

Catabolic Pathway

Example:

Enzyme Structure

Enzymes are catalysts:

The shape of an enzyme depends on the folding of the protein, which itself is determined by the amino acids in the primary structure of the protein, which itself is determined by the DNA genetic code.

Enzymes are GLOBULAR proteins

Propertie	Fibrous Proteins	⛤ Globular Proteins ⛤
Shape
Role
Solubility in Water
Sequence of amino acids
Stability
Examples

Enzymes have an active site to which specific substrates bind.

ACTIVE SITE

SPECIFIC

SUBSTRATE

Some enzymes include a coenzyme or a cofactor.

Both coenzymes and cofactors function by removing electrons, protons or chemical groups from the substrate and passing them to other molecules.

Coenzyme

Cofactor

Enzyme Function

Steps of Enzyme Catalysis

Induced Fit:

Enzymes in anabolic reactions:

Enzymes in catabolic reactions:

Activation Energy

All chemical reactions require ____________________________________________________ to get started

Reactants need to have bonds weakened broken
Molecules need to be reoriented
New bonds need to be formed

The initial energy input in the reaction is called the _______________________________________
Enzymes lower activation energy by

Weakening or breaking bonds in the substrate(s)
Reorienting atoms in the substrate(s)
Forming new bonds

Without enzyme present:

With Enzyme Present:

Enzymes Named in the IB Biology Syllabus

Enzyme Name	Substrate(s)	Product(s)	Location of Reaction
Helicase
Gyrase
Primase
DNA polymerase III
DNA polymerase I
Ligase
RNA Polymerase
tRNA activating enzymes (amino-acyl tRNA synthase)
Taq polymerase
Rubisco
Restriction enzymes (endonucleases)
ATP synthase
Carboxylase
Amylase
Maltase
Lipase
Protease (pepsin)
Protease (trypsin)
Carbonic anhydrase

Temperature, pH, and substrate concentration affect the rate of activity of enzymes

Temperature and Enzyme Activity

Raising temperature generally speeds up a reaction as the particles (in this case enzyme and substrate) move faster and are more likely to collide. However, extreme high temperatures can cause bonds that maintain the structure of the enzyme and its active site to break. As a result, the enzyme will lose its shape (denature) and stop working.

pH and Enzyme Activity

The bonds that maintain the structure of the enzyme and its active site are very vulnerable to changes in pH. Each enzyme has an optimum pH at which it works at its optimum rate. A change in pH causes a change in the shape of the active site, resulting in it being less easy for the substrate(s) to fit in and bind to the active site. The activity of the enzyme is reduced and the rate of reaction slows.

pH and High Temperatures can DENATURE proteins

Denaturation is …

If the bonds are broken, the …

The body strictly regulates pH and temperature to prevent …

Some proteins can …

Substrate Concentration Effect on Enzyme Activity

Increasing substrate concentration increases the rate of reaction to a certain point as there is more opportunity for collision between enzyme and substrate. However, once all of the enzymes have bound a substrate, any more substrate increase will have no effect on the rate of reaction, as the available enzymes will be saturated and working at their maximum rate.

Cells Regulate Metabolism

The overall activity of enzymes, and therefore metabolism, is controlled by a number of factors:

#1 The rate of enzyme production and breakdown.

Sometimes genes are ____________________ (and therefore transcribed) only when an enzyme product is required to catalyze reactions that may occur infrequently, e.g. use of a particular substrate that is not always available.
Other genes are being transcribed all the time because their enzyme products are in ____________________ _________________________, e.g. the genes coding for respiratory enzymes.

#2 Enzyme interaction with the product of the reaction.

_________________________________ operates where high levels of the end product deactivates the enzyme 1 at the beginning of the metabolic pathway
Benefit:

#3 The influence of inhibitors.